Global positioning system (GPS) receiver and method of determining location of GPS receiver

ABSTRACT

A Global Positioning System (GPS) receiver includes a GPS receiving unit configured to receive navigation data from at least one visible satellite, a decoder configured to decode the received navigation data to extract time and almanac information from the decoded navigation data and a database configured to store satellite disposition information. A satellite location determining unit is configured to select at least one visible satellite candidate using the time information and the satellite disposition information, and to determine locations-in-space of the at least one visible satellite candidate with the almanac information. Also, a navigation filter is configured to calculate pseudo-ranges from the at least one visible satellite and the selected at least one visible satellite candidate using the corresponding locations-in-space, and to determine a location of the GPS receiver using the calculated pseudo-ranges.

CROSS-REFERENCE TO RELATED APPLICATIONS

A claim of priority is made to Korean Patent Application No.10-2008-0127436, filed on Dec. 15, 2008, in the Korean IntellectualProperty Office, the subject matter of which is hereby incorporated byreference.

BACKGROUND

The present inventive concept relates to a global positioning system(GPS). More particularly, the present inventive concept relates to a GPSreceiver and positioning method implemented by the GPS receiver.

Generally, GPS was developed to measure locations of objects, typicallyin latitude, longitude and/or altitude. For example, GPS services enablea user to determine his or her location by receiving GPS signals from aconstellation of GPS satellites, measuring information for the currentlocation, and providing the measured information to the user.

In addition, GPS services are utilized for navigation purposes usingadditional data, such as map information, traffic information, and thelike. For example, when a user selects a destination, navigationinformation, such as traffic or direction information from the currentlocation to the selected destination, is provided to the user usingpreviously stored map information. Further, GPS services have beenapplied to various fields, such as military maneuvers, aeronauticaloperations, air traffic control, and the like. In addition to locationinformation, it is possible to acquire time references from GPSsatellites.

GPS services require orbiting GPS satellites for broadcasting GPSsignals, and a GPS receiver for calculating location information inresponse to the received GPS signals. Currently, GPS services depend ona GPS constellation, which includes twenty-four GPS satellites orbitingEarth in different orbits (in particular, twenty-seven GPS satellitesorbit the Earth, three of which are supplemental satellites). In orderto determine its location, the GPS receiver must acquire GPS signalsfrom at least four of the GPS satellites. That is, the GPS receiver mustlock onto signals from four or more GPS satellites.

However, when there is jamming or interference due to other radio wavesor physical obstructions, such as buildings, forests, and the like, theGPS receiver may not be able to lock onto four or more GPS satellites.In this case, the GPS receiver is unable to accurately determine itslocation using GPS services.

SUMMARY

Exemplary embodiments are directed to a GPS receiver and positioningmethods implemented by the GPS receiver, capable of determining thelocation of the GPS receiver when usable signals are received from fewerthan four GPS satellites.

One aspect of the exemplary embodiments provides a Global PositioningSystem (GPS) receiver that includes a GPS receiving unit configured toreceive navigation data from at least one visible satellite, a decoderconfigured to decode the received navigation data to extract time andalmanac information from the decoded navigation data, and a databaseconfigured to store satellite disposition information. The GPS receiverfurther includes a satellite location determining unit configured toselect at least one visible satellite candidate using the timeinformation and the satellite disposition information, and to determinelocations-in-space of the at least one visible satellite candidate withthe almanac information, and a navigation filter configured to calculatepseudo-ranges from the at least one visible satellite and the selectedat least one visible satellite candidate using the correspondinglocations-in-space, and to determine a location of the GPS receiverusing the calculated pseudo-ranges.

Another aspect of the exemplary embodiments provides a method ofdetermining a location of a GPS receiver. The method includes receivingnavigation data from at least one visible satellite; decoding thereceived navigation data to extract time and almanac information fromthe decoded navigation data; selecting at least one visible satellitecandidate using the time information and satellite dispositioninformation stored in the GPS receiver; determining a location-in-spaceof the selected at least one visible satellite candidate using thealmanac information; calculating pseudo-ranges from the at least onevisible satellite and the selected at least one visible satellitecandidate using the locations-in-space of the at least one visiblesatellite and the selected at least one visible satellite candidate; anddetermining a location of the GPS receiver using the calculatedpseudo-ranges.

BRIEF DESCRIPTION OF THE FIGURES

Illustrative embodiments of the inventive concept will be described infurther detail with reference to the attached drawings, wherein likereference numerals refer to like parts throughout the various figuresunless otherwise specified.

FIG. 1 is a block diagram showing a Global Positioning System (GPS)location determination system, according to an embodiment.

FIG. 2 is a block diagram showing a GPS receiver, according to anembodiment.

FIG. 3 is a diagram showing navigation data, according to an embodiment.

FIG. 4 is a diagram showing satellite disposition information, accordingto an embodiment.

FIG. 5 is a table showing right ascension of the ascending node andargument of each satellite.

FIG. 6 is a flow diagram showing operation of a GPS receiver, accordingto an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments will now be described more fully with reference tothe accompanying drawings, in which illustrative embodiments are shown.The inventive concept, however, may be embodied in various differentforms, and should not be construed as being limited only to theillustrated embodiments. Rather, these embodiments are provided asexamples, to convey the inventive concept to one skilled in the art.Accordingly, known processes, elements, and techniques are not describedwith respect to some of the embodiments. Throughout the drawings andwritten description, like reference numerals will be used to refer tolike or similar elements.

According to various embodiments, a GPS receiver is able to determineits own location by receiving and processing information received fromat least one visible satellite, and by additionally selecting one ormore visible satellite candidates based on the information from the atleast one visible satellite, when the number of visible satellites isless than four. A visible satellite candidate is a satellite that ispart of the constellation of satellites, but is not presently visible tothe GPS receiver (e.g., the GPS receiver is unable to lock onto orreceive signals from the satellite).

The GPS receiver is configured to select one or more visible satellitecandidates using previously stored satellite disposition information andtime information, e.g., received from the visible satellite(s), and todetermine locations-in-space of the selected visible satellitecandidates using almanac information received from the visiblesatellite(s).

The GPS receiver according to various embodiments may include any typeof terminal having a GPS module and/or service functionality, such as apersonal digital assistant (PDA), a smart phone, a portable media player(PMP), a navigator, and the like. The embodiments described below assumethat the GPS receiver is able to lock onto or receive GPS signals fromat least one visible GPS satellite.

FIG. 1 is a block diagram showing a GPS location determination system,according to an exemplary embodiment of the inventive concept.

Referring to FIG. 1, The GPS location determination system includes aGPS receiver 10 and multiple GPS satellites 20, 30, 40, and 50. The GPSsatellites 20 to 50 broadcast GPS signals from their respective orbits(about 20,000 km from Earth's surface), and the GPS receiver 10calculates location information for a user based on incoming GPS signalsfrom the GPS satellites 20 to 50. In FIG. 1, four GPS satellites 20 to50 are illustrated for purposes of illustration, although the completeconstellation includes twenty-four GPS satellites rotating Earth inrespective orbits.

Conventionally, the GPS receiver 10 would require four or more visiblesatellites to determine its current location. However, it is assumedthat the GPS receiver 10 in FIG. 1 is able to receive GPS signals fromonly two visible satellites, GPS satellites 20 and 30, and is not ableto receive GPS signals from the remaining satellites, GPS satellites 40and 50. Although the GPS receiver 10 is not able to lock onto four ormore visible satellites, it is still able to determine its locationusing only the GPS signals received from the GPS satellites 20 and 30,according to the various embodiments.

In an embodiment, the GPS receiver 10 locks onto at least one visiblesatellite (e.g., GPS satellite 20 and 30). A GPS signal broadcast fromthe visible satellite may include, for example, navigation data. Inaddition to the visible satellites, the GPS receiver 10 also selects atleast one visible satellite candidate (e.g., GPS satellite 40 and 50) sothat the location of the GPS receiver 10 can be determined. Each of thevisible satellite candidates is a GPS satellite among the multiple GPSsatellites in the constellation having GPS signals that are not receivedby the GPS receiver 10. In this manner, although the GPS receive 10 haslocked onto less than four visible satellites, the GPS receiver 10 stillable to calculate pseudo-ranges between the GPS receiver 10 and GPSsatellites using locations-in-space of four or more GPS satellites byselecting the visible satellite candidates. The GPS receiver 10 is ableto use geometric trigonometry (e.g., trilateration) for positioningcalculations.

FIG. 2 is a block diagram showing a GPS receiver, according to anexemplary embodiment of the inventive concept.

Referring to FIG. 2, the GPS receiver 10 includes a GPS receiving unit100, a decoder 110, a satellite location determining unit 120, anavigation filter 130, a location information output unit 140, anddatabase 150.

The GPS receiving unit 100 is configured to receive and demodulate a GPSsignal from GPS satellites through an antenna. For example, the GPSreceiving unit 100 may receive a GPS signal from a visible satellite,the received GPS signal including a navigation message or navigationdata. The navigation data provides orbit information for determining alocation-in-space of the GPS satellite, as described below withreference to FIG. 3.

The GPS receiving unit 100 outputs the demodulated GPS signal to thedecoder 110, which decodes the incoming GPS signal. That is, the decoder110 is configured to decode the navigation data of the GPS signal andprovides the decoded result to the satellite location determining unit120. The decoder 110, for example, decodes the navigation data of theGPS signal to extract time information, almanac information, ephemerisinformation, etc. The decoder 110 provides the extracted information tothe satellite location determining unit 120.

The time information may include at least one of satellite clockcorrection terms and a GPS week number. The satellite clock correctionterms are used for satellite clock correction and the GPS week numberrefers to a number counted in weekly units. The almanac lamination isorbit information of the satellites and includes information forcalculating locations-in-space of all GPS satellites. The almanacinformation includes a set of parameters for each GPS satellite that canbe used to calculate its approximate location in orbit.

The database 150 stores the satellite disposition information, which isconstellation information regarding the dispositions of the GPSsatellites in their respective orbits, and may be used to determinelocation-in-spaces of the GPS satellites. The satellite dispositioninformation is more fully described with reference to FIG. 4.

The satellite location determining unit 120 determines alocation-in-space of a visible satellite using the decoded navigationdata received from the visible satellite. As stated above, the decodednavigation data may include, for example, time information, almanacinformation, ephemeris information, etc.

The satellite location determining unit 120 is also able to determine alocation-in-space of a visible satellite candidate using the decodednavigation data. In an embodiment, the satellite location determiningunit 120 first selects a visible satellite candidate (e.g., using anidentifier of the visible satellite candidate) based on correspondingsatellite disposition information stored in the database 150 and timeinformation. The satellite location determining unit 120 may select avisible satellite candidate, which is to be used to determine thelocation of the GPS receiver 10, among the GPS satellites other than thevisible satellite(s). Then, the satellite location determining unit 120may determine the location-in-space of the selected visible satellitecandidate using the almanac information.

The satellite location determining unit 120 may select the visiblesatellite candidate(s) such that the total number of visible satellitesand visible satellite candidates is at least four. The satellitelocation determining unit 120 enables the location of the GPS receiver10 to be determined by additionally selecting visible satellitecandidates when the number of visible satellites is less than four. Thesatellite location determining unit 120 provides location information ofthe visible satellite candidate(s) to the navigation filter 130.

The navigation filter 130 calculates a pseudo-range from each visiblesatellite candidate based on information for determining thelocation-in-space of the visible satellite candidate. The navigationfilter 130 also calculates a pseudo-range from each visible satellitebased on the information for determining the location-in-space of thevisible satellite. The navigation filter 130 is then able to determinethe location of the GPS receiver 10 based on the calculatedpseudo-ranges (that is, pseudo-ranges from the visible satellitecandidates and the visible satellites). The navigation filter 130 mayinclude a Kalman filter, for example, which is a recursive filterapplicable to a liner system and is used for real-time processing ofdata associated with the satellites.

The navigation filter 130 may determine not only the location of the GPSreceiver 10, but also the speed of the GPS receiver 10, when the UPSreceiver 10 is actively mobile. The navigation filter 130 provides thedetermined location and/or speed information of the GPS receiver 10 tothe location information output unit 140.

In an embodiment, the location information output unit 140 includes adisplay unit, an audio unit, and the like, for example. The locationinformation output unit 140 is configured to convert the determinedlocation/speed information of the GPS receiver 10 into properlyformatted data (e.g., image or audio formatting, respectively), so thatthe location information may be displayed and/or announced.

The GPS receiver 10 may include a controller (not shown). The controlleris configured to control the operations described above, enabling theGPS receiver 10 to determine its geographic location and/or speed.

When four visible satellites are locked onto, the GPS receiver 10 maydetermine its location using a conventional location determiningprocess. However, when four visible satellites are not locked onto, theGPS receiver 10 must determine its location using the locationdetermining process according to embodiments of the inventive concept.

FIG. 3 is a diagram showing navigation data, according to an exemplaryembodiment of the inventive concept.

Referring to FIG. 3, navigation data may be navigation messages, whichinclude a series of frame (e.g., indicated by representative Frame inFIG. 3). Each Frame may include five subframes, Subframe 1 throughSubframe 5. For example, the Frame in the depicted embodiment consistsof 1,500 bits and has a period of 30 seconds. Each of the Subframes 1through 5 consists of 300 bits and has a period is 6 seconds.

The Subframes 1 through 5 include the following information. The firstsubframe, Subframe 1, includes a GPS week number, space vehicle (SV)accuracy and health, and satellite clock correction terms. The secondsubframe, Subframe 2, and the third subframe, Subframe 3, includeephemeris parameters, respectively. The ephemeris parameters provide theorbital information of the satellite's orbit, which is recorded overtime. The ephemeris may be used to predict subsequent orbit and/orshifts in orbit of the corresponding satellite. The ephemeris parametersare recorded every 30 seconds, for example, and consist of 16 keplerianelements. Thus, the ephemeris parameters are not used after a certaintime elapses.

The fourth subframe, Subframe 4, includes almanac and health data forsatellites 25 to 32, special messages, satellite configuration flags,and lonospheric and Coordinated Universal Time (UTC) data. The fifthsubframe, Subframe 5, includes almanac and health data for satellites 1to 24 and almanac reference time and week number. Each of Subframes 4and 5 consists of 25 pages, which is the amount of data used to acquireaccurate almanac data. The almanac data includes general information forall satellites.

The first to fifth subframes, Subframes 1 through 5, include telemetry(TLM) as information for frame acquisition and hand-over word (HOW) as ahandover flag for inter-satellite handover, respectively. It is possibleto determine the orbital position of one or more visible satellitesusing time data in Subframe 1 and almanac data in Subframes 4 and 5.

FIG. 4 is a diagram showing satellite disposition information, accordingto an exemplary embodiment of the inventive concept, and FIG. 5 is atable showing the right ascension of the ascending node (RAAN) andargument of each satellite.

Referring to FIG. 4, satellite disposition information is the orbitalposition information for each of the GPS satellites in the GPS satelliteconstellation, including locations-in-space of the respective GPSsatellites. The satellite disposition information is location-in-spaceinformation for each GPS satellite determined on the basis of RAAN andlatitude parameters.

In FIG. 4, the generally vertical axis indicates the argument oflatitude relative to the equator, and the horizontal axis indicates sixorbit planes A to F. Each orbit plane includes four GPS satellites, andthe six orbit planes include twenty-four GPS satellites. The horizontalaxis may be used to illustrate the RAAN of each satellite, asillustrated in FIG. 5.

In FIG. 5, a slot indicates an identifier (or index) of each satellite,and symbols A to F included in a satellite identifier of each satelliteindicates a corresponding orbit plane in which the satellite is located.FIG. 5 illustrates the RAAN and argument of latitude of each GPSsatellite.

Accordingly, the satellite disposition information may be constellationinformation for satellite disposition in FIG. 4 or the RAAN and argumentof latitude of a corresponding GPS satellite, as illustrated in FIG. 5.The satellite disposition information may include location-in-spaceinformation for all or part of the GPS satellites.

FIG. 6 is a flowchart showing operation of a GPS receiver, according toan exemplary embodiment of the inventive concept.

Referring to FIG. 6, a GPS receiver (e.g., GPS receiver 10 in FIG. 1)performs an initializing operation in block 1000. In block 1010, the GPSreceiver searches visible satellites. For example, the GPS receiver maysearch GPS signals received from GPS satellites (e.g., GPS satellites 20and 30 in FIG. 1), which may be the visible satellites with respect tothe GPS receiver.

In block 1020, the GPS receiver determines whether the number of visiblesatellites located pursuant to the search is less than four. When thenumber of visible satellites is less than four, the GPS receiverperforms a location determining process in accordance with embodimentsof the present inventive concept, proceeding to block 1030.

In block 1030, the GPS receiver determines whether the number of visiblesatellites is less than one (i.e., there are no visible satellites).When the number of visible satellites less than one, the process returnsto block 1000, since the GPS receiver must be able to lock onto signalsfrom at least one visible satellite in order to determine its location.

When the number of visible satellites is not less than one, the GPSreceiver decodes navigation data in the signals received from thevisible satellites in block 1040. The decoded navigation data mayinclude frame information, as illustrated in FIG. 3, for example.

In block 1050, the GPS receiver determines the locations-in-space of thevisible satellites based on the navigation data. Since each visiblesatellite is a GPS satellite having GPS signals received by the GPSreceiver, it is possible to directly determine the location-in-space ofthe visible satellite using the navigation data received from the GPSsatellite.

In block 1060, the GPS receiver selects visible satellite candidatesusing time data extracted from the navigation data and satellitedisposition information stored in the GPS receiver. More particularly,the GPS receiver selects identifiers of the visible satellitecandidates.

In block 1070, the GPS receiver determines the locations-in-space of theselected visible satellite candidates. For example, the GPS receiver maydetermine the locations-in-space of the selected visible satellitecandidates using almanac data, which is extracted by decoding thenavigation data received from the visible satellites. The total numberof visible satellites and visible satellite candidates may be four ormore.

In block 1080, the GPS receiver calculates a pseudo-range of each of thevisible satellites and visible satellite candidates when thelocations-in-space of the visible satellites and visible satellitecandidates have been determined. The GPS receiver may calculate thepseudo-range using the locations-in-space of the visible satellites andthe visible satellite candidates, respectively.

Returning to block 1020, when the number of visible satellites is morethan four, the GPS receiver is able to perform a conventional locationdetermining process, proceeding to block 1090.

In block 1090, the GPS receiver decodes the navigation data from thevisible satellites. In block 1100, the GPS receiver updates satellitedisposition information, stored in a database, with informationextracted from the decoded navigation data. In various embodiments, theupdating of block 1100 may be performed selectively by the GPS receiver.

The GPS receiver determines the locations-in-space of the visiblesatellites using the navigation data in block 1110. In block 1120, sincethe visible satellites are GPS satellites having GPS signals received bythe GPS receiver, the locations-in-space of the respective visiblesatellites may be determined directly using the navigation data receivedfrom the GPS satellites.

The GPS receiver calculates pseudo-ranges from the respective visiblesatellites in block 1120. For example, the GPS receiver may calculatethe pseudo-ranges using locations-in-space of the visible satellites.

In block 1130, the GPS receiver determines its own location and/or speedusing the calculated pseudo-ranges, using either the pseudo-ranges fromthe visible satellites and visible satellite candidates calculated inblock 1080 or the pseudo-ranges from only the visible satellitescalculated in block 1120. The UPS receiver then outputs the locationinformation in block 1140. In an embodiment, outputting the locationinformation in block 1140 is optional.

In block 1150, the GPS receiver determines whether to terminate thelocation determining. When the location determining operation is not tobe terminated, the process returns to block 1010. When the locationdetermining operation is to be terminated, the process ends.

In accordance with embodiments of the location determining operation ofa GPS receiver, it is possible to determine the location of the GPSreceiver, even though the GPS receiver has not locked onto at least fourvisible satellites, by selecting and calculating locations-in-space forvisible satellite candidates. Accordingly, performance does not sufferwhen the number of visible GPS satellites is otherwise not enough forlocation determination.

While the present inventive concept has been described with reference toexemplary embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the present teachings. Therefor, it shouldbe understood that the above embodiments are not limiting, butillustrative.

What is claimed is:
 1. A Global Positioning System (GPS) receiver,comprising: a GPS receiving unit configured to receive navigation datafrom at least one visible satellite; a decoder configured to decode thereceived navigation data to extract time and almanac information fromthe decoded navigation data; a database configured to store satellitedisposition information; a satellite location determining unitconfigured to select at least one visible satellite candidate using thetime information and the satellite disposition information, and todetermine locations-in-space of the selected at least one visiblesatellite candidate using the almanac information; and a navigationfilter configured to calculate a pseudo-ranges from the at least onevisible satellite and the selected at least one visible satellitecandidate using the locations-in-space of the at least one visiblesatellite and the selected at least one visible satellite candidate,without the GPS receiving unit receiving signals from the at least onevisible satellite candidate, and to determine a geographic location ofthe GPS receiver using the calculated pseudo-ranges.
 2. The GPS receiverof claim 1, wherein the time information comprises at least one ofsatellite clock correction terms and a GPS week number.
 3. The GPSreceiver of claim 1, wherein the satellite disposition informationcomprises satellite constellation information includinglocations-in-space of all satellites in the satellite constellation. 4.The GPS receiver of claim 1, wherein the total number of the at leastone visible satellite and the at least one visible satellite candidateis at least four.
 5. The GPS receiver of claim 1, wherein the satellitelocation determining unit is further configured to determine alocation-in-space of the at least one visible satellite using thedecoded navigation data.
 6. A method of determining a location of aGlobal Positioning System (GPS) receiver, the method comprising:receiving navigation data from at least one visible satellite of aplurality of GPS satellites; decoding the received navigation data toextract time and almanac information from the decoded navigation data;selecting at least one visible satellite candidate of the plurality ofGPS satellites using the time information and satellite dispositioninformation stored in the GPS receiver; determining a location-in-spaceof the selected at least one visible satellite candidate using thealmanac information from the received navigation data; calculatingpseudo-ranges from the at least one visible satellite and the selectedat least one visible satellite candidate using the locations-in-space ofthe at least one visible satellite and the selected at least one visiblesatellite candidate without the GPS receiving unit receiving signalsfrom the at least one visible satellite candidate; and determining ageographic location of the GPS receiver using the calculatedpseudo-ranges.
 7. The method of claim 6, wherein the time informationincludes at least one of satellite clock correction terms and a GPS weeknumber.
 8. The method of claim 6, wherein the satellite dispositioninformation comprises satellite constellation information includinglocations-in-space of all satellites in the satellite constellation. 9.The method of claim 6, wherein the total number of the at least onevisible satellite and the selected at least one visible satellitecandidate is four or more.
 10. The method of claim 6, further comprisingdetermining a location-in-space of the at least one visible satelliteusing the decoded navigation data.